No, ArcPad does not support NULL values. The issue arises with the DBF tables associated with the data. The concept of NULL does not exist in a DBF. It is recommend that the user update their database design to model NULL values in a different way that ArcPad supports. For example, say the field is DISTANCE. You can introduce a CHAR (1) field called DISTANCE_NULL which is set to be ‘Y’ or ‘N’.